Acoustical tactics for the 2nd regionProblematic
room modes cannot be eliminated in the acoustical small room.
They can only be managed. This can initiate by designing
or selecting a room with dimensions that produce a more even
distribution of room modes. The
following ratios from the Master
Handbook of Acoustics will
assist:

HandbookNote: Do not panic if your room does not meet this room ratio criteria. You can still make it work.

If
you are of a curious nature, draft a room mode analysis of the
proposed room to expose any potential room mode issues.
Locate modes
below 300 Hz and analyze their spacing. Identify
coincidencesand
isolated modes spaced more than 20 Hz. For
the
less curious skip to
the next paragraph.

Create
an illustration of the room mode peak and null points of F1 throughF3 on the proposed floor
plan. Note that the points are equal to the length and
width dimensions divided and even number. The floor plan sketch will be used for speaker and listener placement.

This is it -- the Mounkes speaker listener placement method
Steve Mounkes was my friend and a
reference for the word audiophile. He is missed. Long ago
he taught me this simple speaker/listener placement method.
This plus a modest dose of room treatment (carpet, drapery, book filled shelves) delivers substantial audio improvement. If I had to pick one
practical audio application from this Handbook -- this is it.

1. Divide the room
width by the values 3,
5, 7,
and 9. With the results; measure
and mark these points along
the
width of the room from the front left
corner and
then the right corner.

2. Next,
divide
the room length
by the same values. Mark these points along the room
length
from
the front left and
right corners.

Then select the stereo corner stonesObserve
the on-floor coordinates
established by the width and length points. While avoiding the room mode peaks and null points of your F1 thru F3 sketch; select a pair of practical
coordinates for the left
and right
speakers.
Then place the listening
position in
an equilateral triangle with the speakers.

Surround soundA
multi-channel surround
sound system is a
circular configuration that
introduces additional
speakers onto the stereo arrangement. Its radius
is the distance from the listening position to the left/right
speaker locations. Therefore place the center
channel
speaker
on the radius mid-point between the front left and right positions.

Choose
rear
speakerpositions.
- In a 5.1 surround
sound arrangement; place
rear speakers at 110°
left and right of the front center
speaker.

- In a 6.1
arrangement; add an additional speaker
to the 5.1
arrangement at 180°
of the front center speaker.

- In a 7.1
THX arrangement; add two additional rear speakers to the 5.1
arrangement at 150°
left and right of the front center
channel.

The
listening position of the equilateral triangle is the ideal seating
location. However, additional seating is probably desirable.
Therefore, carefully select additional positions that are
comfortable
and practical, but avoid room mode peaks and null points.

Subwoofer placementFinally,
while evading peak and null points; select the placement
for the sub
woofer. If the sub woofer is placed sufficiently
away
from the room boundary, but less than ¼ of the dimension, it will
minimize stimulating modes F1 thru F4. Chapter Six page 5 offers more detailed instructions.

If
troublesome distorting room
modes audibly persist; then absorb them with the placement of a broad bandwidth
bass
trapin
the corner
nearest each speaker.

In
the final analysis subjectively fine-tune all speaker and listener
positions with the organic sound meter that is attached to your
head.
It is still the most sensitive listening device available.